1. Field of the Invention
The present invention relates to a steam engine that converts thermal energy into mechanical energy.
2. Description of the Related Art
A heat power plant and the like utilize a steam engine based upon a Rankine cycle in which a generated superheated steam is isentropically expanded in a steam turbine to extract mechanical energy. Then, the steam expanded in the steam turbine is cooled and condensed. Condensed liquid is isentropically compressed and heated for vaporization, to regenerate the superheated steam.
In the above steam engine, the degree of superheat of the steam increases before expansion for the purpose of preventing part of the steam from liquefying due to a decrease in dryness of the working fluid in the steam turbine when the steam is isentropically expanded therein. However, as shown in a T-s diagram (temperature-entropy diagram) of FIG. 12, it is difficult to perfectly prevent the emergence of water droplets in the steam turbine.
In a converting process of expansion energy of the steam turbine and the like into mechanical energy, the emergence of the water droplets induces corrosion and abrasion in a part that receives steam pressure, such as a turbine blade, a piston, and the like. Accordingly, in the steam engine (a motive power plant) using the Rankine cycle, the steam must be generally expanded in such a manner that the dryness does not decrease to 90% or less. Therefore, it is difficult to increase the mechanical energy taken out of the thermal energy, that is, to efficiently convert the energy.